Geometric crystal class

From Online Dictionary of Crystallography

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Classe cristalline géométrique (Fr); Geometrische Kristallklasse (Ge); Clase cristallina geométrica (Sp); Classe cristallina geometrica (It); 幾何的結晶類 (Ja).


Geometric crystal classes (or simply 'crystal classes') classify the symmetry groups of the external shape of macroscopic crystals, namely according to the morphological symmetry. There are 10 two-dimensional geometric crystal classes and 32 three-dimensional geometric crystal classes, in one to one correspondence with the 10 and 32 types of point groups in E2 and E3, respectively.

Japanese nomenclature

The Japanese term commonly used to indicate a crystal class is 晶族 which however, as pointed out by Matsumoto (1977), is not an appropriate translation in that the character 族 is more suitable to indicate a crystal family. According to this author, a better translation of crystal class is 結晶類, which is therefore adopted in this dictionary.

See also

  • Arithmetic crystal class
  • Section 8.2.4 of International Tables for Crystallography, Volume A
  • Matsumoto, T. (1977). J. Miner. Soc. Japan, 13, 247-289.